Electromagnetic interference (EMI) is the generation of undesired electrical signals in electronic system circuitry when an electromagnetic (EM) wave in one electrical circuit, component or part is unintentionally transferred to another electrical circuit, component or part. As the size of electronic systems decreases, the density of electrical components in these systems increases, and the dimensions of circuit elements correspondingly decrease. As spacing decreases between circuit elements, the likelihood of interference from adjacent circuit elements increases. EMI is a common issue for most high frequency electronic products. With the increased circuit densities along with increased data rates, it is increasingly difficult to meet regulatory electromagnetic compatibility (EMC) requirements.
Electronic product manufacturers take several approaches to minimizing EMI for EMC compliance. Shielding products to prevent EM radiation is a common technique. At the system or board level metal cages or metal covers may be installed to prevent the radiation of electromagnetic waves causing EMI. While commonly done, this can be an awkward and costly solution to meeting EMC requirements. In smaller, portable devices running with higher frequencies, metal covers or shields may be hard to implement. In printed circuit board (PCB) design, placement of high frequency devices may be planned to avoid devices sensitive to EMI. Careful device placement may reduce the size of card covers used to reduce EMI. Designs that focus on suppression of unwanted electromagnetic radiation can provide a more cost effective solution to reducing EMI. Suppression of EMI before is it transmitted outside of the system or enclosure is critical to EMC compliance.
The generation of excess EM radiation in devices is problematic to other components within the electronic device and to other nearby electronic devices. Unwanted signals generated from excess EM radiation, from within a device and from nearby electronic devices, leads to EMI in electronic devices. For this reason regulatory committees exist both nationally and internationally to monitor and define limits of allowable EMI for various electronic devices. Requirements and tests are defined for EMC that monitor EM radiation causing EMI between systems and components for electronic devices.